1. Field of the Invention
This invention relates to an electronic component having a contact for brazing and a method of manufacturing the same, and particularly to a novel method of forming on the contact an arresting region for arresting a weld brazing material from creeping up or climbing up a finish plating layer formed on the contact which layer is a film highly wettable to the weld brazing material, and to an electronic component having such arresting region.
2. Description of the Related Art
The related prior art will be described with reference to FIGS. 1 and 2.
An electronic component 10 comprises a contact 11 and a holder 12 of insulating material molded integrally with the contact 11 so as to hold it. The contact 11 comprises a terminal section 111 to be brazed to a plating layer 21A formed around the inner peripheral surface of a through-hole 21 which is formed through a wiring board 2, and a contact section 112 adapted to electrically contact with another electronic component. A strip of weld brazing material 3 such as solder is pre-applied to a brazing pad 22 which is connected to a wiring conductor (not shown) formed on the undersurface of the wiring board 2.
The terminal section 111 of the contact 11 has its surface plated with tin or gold which is a material highly wettable to the weld brazing material. With such plated terminal section 111 inserted in the through-hole 21 coated with the plating layer 21A (FIG. 1), the weld brazing material 3 applied to the undersurface of the wiring board 2 is heat-fused to electro-mechanically connect the terminal section 111, the through-hole plating layer 21A and the brazing pad 22 together by means of brazing whereby the terminal section 111 is mounted to the wiring board 2 to constitute the electronic component 10.
During this brazing process, as the heat-fused weld brazing material 3 is drawn up (which will be referred to as “creeping up” hereinafter) along the terminal section 111 beyond the upper surface of the board 2 while wetting the highly wettable plating layer of the surface of the terminal section 111, the amount of the weld brazing material 3 is correspondingly reduced in the bonding region between the terminal section 111 and the through-hole plating layer 21A. As the heating is repeated a plurality of times, the weld brazing material will run short, ultimately leading to incomplete electro-mechanical connection between the terminal section 111 and the through-hole plating layer 21A.
One approach proposed to solving the problem of shortage of the weld brazing material between the terminal section 111 of the contact 11 and the through-hole 21 due to the creeping-up of the brazing material is to form an oxide film region 113 on the terminal section 111 by oxidizing a corresponding surface portion thereof so that the oxide film region 113 serves as means for arresting the creeping-up of the weld brazing material 3 on a portion of the terminal section 111 (refer to the Published Japanese Patent application No. 8-213070 for particulars).
Specifically, the oxide film region 113 is shaped in a band shape and formed around the terminal section 111 of the contact 11 where the heat-fused weld brazing material 3 can creep up, by oxidizing at a corresponding band portion of the highly wettable tin plating or gold plating layer of the terminal section 111. The oxide film region 113 in a band shape thus obtained by oxidation of the surface plating layer is poorly wettable with respect to the weld brazing material 3, so that the heat-fused weld brazing material 3 may not overreach.
However, since this oxide film is nothing more than what is produced by oxygen atoms combining with atoms of the tin or gold forming the surface layer of the terminal section, it is not possible to visually determine whether the surface of the tin plating or gold plating layer deposited on the surface of the terminal section 111 has actually been treated by formation of an oxide film or whether the treatment by oxide film formation has been effected in proper location and geometry on the terminal section 111.
Illustrated in FIGS. 3a–3c is another example of the prior art approach to solving the problem of shortage of the weld brazing material at the terminal section of the contact, in which a nickel plating layer 11A is formed as a primer layer over the entire surface of the contact 11, followed by coating the contact section 112 with a relatively thick gold plating 112A of 0.4 μm thickness while coating the terminal section 111 with a relatively thin gold plating layer 111A of 0.05 μm thickness for brazing use, with a predetermined spacing (0.3 mm) between the coated contact section 112 and terminal section 111 to leave therebetween an exposed section of the nickel plating layer, which is then transformed into a nickel oxide layer 113′ by anodic oxidation to define an arresting region for arresting the creeping-up of the molten weld brazing material (refer to the Published Japanese Patent Application No. 10-247535 for particulars).
This nickel oxide layer 113′ is a poorly wettable region, which the heat-fused weld brazing material 3 cannot overreach to thereby be prevented from creep up and migrate any further.
Nevertheless, in the prior art example of FIGS. 3a to 3c it is difficult to reduce the width of the nickel oxide layer 113′ to as narrow as less than 0.2 mm.
Processing with the use of liquid (such as plating and coating) is inferior in accuracy in controlling the location and area where such processing is to be conducted. Especially, the plating process requires the operations of controlling the liquid level and using a tape or a jig for masking, leading to deterioration in the accuracy in the location where the plating region is to be formed. Consequently, it is difficult to conduct the plating process consistently with tolerances less than 1 mm.
Specifically, the accuracy in the location and width of the portion of the nickel layer which should be left bare is not so high, since it is affected by the working accuracy both in the location where the gold plating layer is applied on the contact section 112 and in the location where the gold plating layer for brazing is applied on the terminal section 111. This can make the volume production infeasible for minute electrical terminals having a terminal length less than 2 mm.
In addition, the oxide film thus formed cannot be visually determined as to whether the treatment has been actually completed or not. Similar problems would also arise in the case where the formation of a nickel oxide layer by anodizing is conducted prior to the formation of the gold plating layer on the contact section 112 and the gold plating layer for brazing on the terminal section 111.
As will be appreciated from the foregoing discussion, the ‘creeping-up’ problem of the weld brazing material 3 in the contact as illustrated in FIGS. 1–3 has not yet been eliminated.
Similar problems are involved also with still another type of contact, as will be discussed below.
Referring to FIG. 4a, there is shown another example of the prior art in which a wiring board 2 has formed on its surface a brazing pad 22 on which is deposited a weld brazing material 3 which is adapted to be heat-fused to braze a terminal section 111 of a contact 11 to the brazing pad 22.
In this example of the prior art as well, when the weld brazing material 3 is heat-fused, it is drawn up along the surface 111A of the terminal section 111 while wetting the surface 111A of the terminal section 111 as shown in FIG. 4b until it rises up to the contact section 112 to wet the surface 112A thereof as shown in FIG. 4c, whereby the weld brazing material 3 is correspondingly short in the bonding region between the terminal section 111 and the brazing pad 22. The line B shows a boundary line between the surfaces 111A and 112A.